The invention relates to improvements in methods of and in apparatus for controlling the operation of driving systems for various types of machines, such as packing machines for cigarettes or other articles of the tobacco processing industry. More particularly, the invention relates to improvements in methods of and in apparatus for controlling the operation of driving systems of the type wherein a rotary main drive (e.g., an electric motor) is electrically connected with one or more slave drives (e.g., servomotors) each of which can be used to transmit motion to a discrete movable part, or to a group of movable parts, in a machine. Still more particularly, the invention relates to improvements in methods of and in apparatus for controlling the operation of driving systems wherein the angular position of the rotary main drive is monitored and the operation of the sleve drive or drives is regulated in dependency on the angular positions of the main drive. The invention will be described with reference to packing machines for articles of the tobacco processing industry with the understanding, however, that the improved method and apparatus can be put to use with equal or similar advantage to control the operation of driving systems for other types of machines, for example, machines for packing articles other than those belonging to the tobacco processing industry, paper sheet forming, stacking and wrapping machines and/or others.
A modern cigarette packing machine is equipped with a number of units each of which has one or more movable parts, and such movable parts are called upon to operate in synchronism while moving relative to each other in order to ensure rapid, reliable and predictable gathering of arrays of cigarettes, introduction of arrays into packets, closing and sealing of the packets, application of revenue labels to the closed and sealed packets, confinement of labelled packets in envelopes of light transmitting plastic material, confinement of groups of packets in cartons and introduction of cartons into boxes for storage or for transport to customers. It is important to ensure that the movable parts will not clash and thus damage each other because any, even short-lasting, stoppage of a modern high-speed packing machine would entail huge losses in output. Furthermore, stoppage of a modern packing machine necessitates stoppage of all other machines in a complete production line which further increases the losses. Therefore, it is important to ensure that the various movable parts of a cigarette packing machine are free to move relative to each other, that such parts are operated in synchronism to guarantee that the machine can turn out large numbers of high-quality packets, cartons and boxes per unit of time, as well as that the moving parts are operated by a compact driving system which can accurately determine the times of operation and idleness of various movable parts.
Examples of movable parts which are utilized in a cigarette packing machine are endless belt conveyors, endless chain conveyors, indexible turret conveyors, prongs, pushers, jaws, tongs, plungers, folding fingers and many others. In certain packing machines, all or a large majority of such movable parts receive motion from a main drive through the medium of transmissions which are operated by the main drive and transmit rotary, reciprocatory and/or other movements to the respective discrete movable parts or groups of movable parts. The transmissions can be used to impart to the respective parts continuous or intermittent, regular or irregular movements, either directly or by utilizing cam and follower units.
It is also known to employ in a cigarette packing machine a driving system wherein a main drive (such as a rotary electric motor) drives a plurality of slave drives and each slave drive transmits motion to one or more movable parts of the machine. The connection between the main drive and the slave drives can be of the type known as an electric or electronic shaft which is preferred in many instances because it ensures that the slave drives are operated in exact synchronism with the main drive when such mode of operation is desirable or advantageous.
A drawback of presently known driving systems of the just outlined character (i.e., systems employing a main drive and a set of slave drives which are electrically connected to the main drive) is lack of sufficient flexibility. Such conventional driving systems operate quite satisfactorily as long as the operation of one or more slave drives need not be interrupted or otherwise altered. On the other hand, it is often necessary to interrupt the operation of one or more slave drives, for example, in order to rapidly or immediately segregate defective arrays of cigarettes so that the defective arrays are expelled prior to undergoing any, or prior to undergoing extensive, additional treatment including introduction into packets, closing and sealing of packets containing defective arrays of cigarettes, the application of revenue labels to closed and sealed packets which contain defective arrays of cigarettes, and so on.